This invention relates to a method of controlling electrical devices of an internal combustion engine, and more particularly to a method of controlling energization time periods of the electrical devices which control an operation of an internal combustion engine by the use of an interrupt signal from time-counting means.
Conventionally, in order to control a plurality of electrical devices which control an operation of an internal combustion engine, e.g. fuel injection valves (injectors), a method is known which employs a plurality of time-counting means provided respectively for the electrical devices, for counting energization periods of time thereof, respectively, and each outputting an interrupt signal when the counting of the energization period of time is completed, and a central processing unit for computing the energization periods of time in response to operating conditions of the engine, outputting a counting starting signal for each of the time-counting means when the computing is completed and at the same time outputting an energization starting signal for each of the corresponding electrical devices, and outputting an energization ending signal for each of the electrical devices in response to the interrupt signal from the time-counting means.
However, this known method requires the use of as many time-counting means as the electrical devices, and this brings about the problem of a high manufacturing cost of the electrical device-controlling system.
On the other hand, even if the control of the engergization periods of time of the electrical devices is attempted by the use of a single time-counting means in order to overcome the above disadvantage, it becomes impossible to control the electrical devices properly since there may arise a condition under which two or more electrical devices simultaneously operate (hereinafter referred to as "the overlap condition"). Under the overlap condition the electrical devices must be controlled in such a manner that before the operation of one electrical device is ended, the operation of another electrical device is started.
Further, it is usually designed that the central processing unit carries out not only the computation for the control of the electrical devices but also a number of computations necessary for other kinds of control, and to this end it is provided with a specific time interval during which the control of the electrical devices is not started by an interrupt signal from the time-counting means (hereinafter referred to as "the interrupt-inhibit interval"). Therefore, if an interrupt signal from the time-counting means is produced at a time corresponding to the interrupt-inhibit interval, the interrupt is inhibited until the interrupt-inhibit interval terminates. This interrupt inhibition applies even in the case of a single electrical device. Consequently, the outputting of the energization ending signal for an electrical device is delayed by the time elapsed before the interrupt-inhibit inverval terminates. As a result, the energization period of time of the electrical device is virtually prolonged, which makes it impossible to control the actual energization period of time to a desired value determined in response to operating conditions of the engine, and therefore to secure desired driveability, fuel consumption, etc.